This invention relates in general to insulation products made from fibrous glass. Fibrous glass insulation products generally comprise randomly-oriented glass fibers bonded together by a cured thermosetting polymeric material. Molten streams of glass are drawn into fibers of random lengths and blown into a forming chamber where they are randomly deposited onto a traveling conveyor, growing in thickness to become a fibrous pack. The fibers, while in transit in the forming chamber and while still hot from the drawing operation, are sprayed with an aqueous dispersion or solution of binder. A phenol-formaldehyde binder has been traditionally used throughout the fibrous glass insulation industry, although acidic, formaldehyde-free binders are also known. The residual heat from the glass fibers and from the flow of hot gases during the forming operation is sufficient to vaporize much of the water from the binder, thereby concentrating the binder dispersion and depositing binder on the fibers as a viscous liquid with high solids content. Further water may be removed by drying the binder on the fibers. The uncured fibrous pack is transferred to a curing oven where heated air, for example, is blown through the pack to cure the binder and rigidly bond the glass fibers together in a generally random, three-dimensional structure. Sufficient binder is applied and cured so that the fibrous pack can be compressed for packaging, storage and shipping, yet regains its thickness—a process known as “loft recovery”—when installed.
Viscous binder dispersions, whether in initial state or as the aqueous medium vaporizes, tend to be tacky or sticky and hence they lead to accumulation of fiber and binder solids on the forming chamber walls and other equipment. This accumulated fiber and/or binder resin solids may later fall onto the pack causing dense areas or “wet spots” and other product problems. In the case of acidic binders, accumulation on forming equipment and related components can also cause corrosion.
There have been a variety of attempts to address this corrosion problem. For example, some manufacturers have replaced carbon steel in the forming and washwater equipment with stainless steel. However stainless steel equipment is expensive relative to equipment made of carbon steel. Another proposed solution has been to decrease the amount of cycles that the washwater is introduced through the forming equipment. However, this also leads to increased costs in terms of water usage and wastewater removal. U.S. Pat. No. 7,754,020 to Cline, et al. discloses a method of reducing acid corrosion of the surfaces of equipment used to form fiberglass insulation, by using two distinct washwater systems. One system reclaims washwater from the forming chamber wall only and recycles it either for subsequent chamber wall wash cycles, or for mixing with binder solutions, in which case acid may be added to lower the pH. The second washwater system reclaims water from other areas of the forming operation and the pH of this water may be adjusted upward by adding base to the washwater when the pH drops below about 8.